The invention relates to a control button unit with a block element design, and more particularly to a control button unit of the type which includes a housing mountable in a supporting wall and a hollow plunger which can be returned by means of a spring, the outer end of the plunger being designed as a pushbutton that is illuminable from inside. A coupling piece having several plug locations receives block elements that are arranged in parallel and next to one another. Among other things, a block element may be designed as a switching element with a movable member which is mounted so as to be displaceable in the direction of movement of the plunger and which is actuable by the plunger, the switching element having at least one set of contacts. A block element may also be designed as a lighting element with a lampholder or other light source.
A known control button unit of this type is sold under the trademark RAFIX S 22 by Messrs. Rafi GmbH & Co. The actuator of this control button unit has a round pushbutton, and the coupling piece has three plug locations. The switching elements are designated as contact elements. Their movable members have a flat end projecting at the top and each carries a contact bridge which acts as a break contact or a make contact, depending on the type of switching element in question. The connecting terminals are located on the underside facing away from the observer. The lighting element, which can only be attached at the middle plug location of the coupling piece, merely contains the connecting terminals for the lampholder placed on top.
Because of the hollow round form of the plunger which is necessary for receiving the lamp and lampholder to illuminate the pushbutton, the plunger only reaches the movable members of the switching elements when these are inserted in the outer plug locations. It is possible to do without the lighting element and a third switching element can be inserted in the middle plug location instead of the lighting element, but a special thrust piece then has to be inserted into the plunger. The special thrust piece is needed in order to fill the end face of the plunger in the center so that the movable member of the middle switching element can also be reached and moved by the plunger.
Control button units of this type may be used for the manual control of motor drives with opposite directions of rotation, for example to open and close a gate. As is customary, for each direction of rotation there is a control button unit which is equipped with a "break" switching element and a "make" switching element. In such cases, the break contact in the "right-rotating" control button unit breaks the circuit for rotation to the left, and vice versa (electrical locking). A problem may arise since the working contact bridge may become welded to its counter-contact pieces and jam when the pushbutton is released. However, the break contact contained in the other switching element returns to its position of rest and therefore no longer performs its locking function. The known control button unit is thus unsuitable for switching arrangements in which specific interdependences between the individual switching elements have to be taken into account.
There is often a need, in the control button units described and in similar ones, to actuate the switching elements not by touch engagement, but by locking engagement, so that the contact sets are brought into one position by pressing on the pushbutton and, after the pushbutton has been released, are brought into the other position by exerting pressure again. It is known from German Patent Specification No. 1,169,549 and, without actual proof, also from control button units with a block element design, to accommodate the mechanism for the so-called high and low locking in the actuator. The result of this is that an actuator without this mechanism and one with this mechanism have to be kept in stock. A further disadvantage of this known construction is that, if it becomes necessary at a later stage to change the switching function from locking engagement to touch engagement, or vice versa, the actuator built into the supporting plate has to be exchanged, and this is extremely troublesome. Also, all the contact sets can only be actuated either by touch engagement or by locking engagement (no mixture).